We report a rare location of a PMT involving the craniofacial sinuses of the skull base. The typical laboratory findings secondary to phosphate loss are hypophosphatemia and hyperphosphaturia, which finally result in an inadequate mineralization of osteoid in mature bone, a metabolic disorder known as osteomalacia. Oncogenic osteomalacia is dramatically cured by tumor removal but when the tumor is not detected this condition can respond to 1,25 dihydroxyvitamin and phosphate supplementation. Phosphaturic mesenchymal tumor is usually located in soft tissue, but intraosseus as well sinonasal locations are also on record. Histologically, it corresponds to a polymorphous group of neoplastic entities (1
), the most common of which is the so-called “mixed connective tissue type” (1
), which is characterized by a distinctive admixture of bland spindled cells, osteoclast-like giant cells, microcysts, prominent and variously sized vasculature, smudgy to calcified cartilage-like matrix, and metaplastic bone. Other histological types of phosphaturic mesenchymal tumors are the osteoblastoma-like tumor, the non-ossifying fibroma-like tumor and the ossifing fibroblastoma-like tumor. Some cases have histological features of malignancy (6
To date, a total of 142 cases are on record in the literature (7
), of which only 11 cases were located in the nasal fossa and craniofacial sinuses ().
Table 1 Reported cases of phosphaturic mesenchymal tumors located in the nasal fossa and craniofacial sinuses (8–16).
Phosphaturic mesenchymal tumor (PMT) is an uncommon, distinctive tumor that is frequently associated with oncogenic osteomalacia, itself a rare paraneoplastic syndrome. Sinonasal PMT is the rarest variant with its own peculiar histologic features, often differs from the mixed connective tissue type, and more closely resembles a sinonasal hemangiopericytoma-like variant (1
). PMT is usually a benign tumor, but some cases of malignant transformation have been described (7
). Metastatic disease has also been reported (malignant connective tissue variant) (7
). Osteogenic osteomalacia – the clinical effect of the tumor – is vitamin D resistant, and is dramatically cured by tumor removal.
PMT is usually located in soft tissue, but intraosseous as well as sinonasal locations have also been reported. In Folpe et al.’s own series of PMT, 18 out of 32 total cases occurred in soft tissue, nine in bone and two in paranasal sinuses, including the present one (2
). Patients are usually in their adulthood at the time of diagnosis, but pediatric cases have also been reported (age range: 5 to 63 years). Any site can be affected, with the lower extremities being the most common (40–50% of cases), followed by the head and neck area (15–20%), trunk (15–20%) and upper extremities (around 10%). Unusual locations (e.g. big toe) are not uncommon. Tumor size is variable, ranging from 1 cm to 15 cm, with a median size of 5.6 cm for soft tissue location (3
). Somatostatin receptor imaging has been recently proved to improve the detection of such tumors, based on the postulate that such tumors express somatostatin receptors (5
In conclusion, PMT is a rare pathologic entity that is poorly understood by pathologists, clinicians and radiologists. PMT of craniofacial sinuses has peculiar histological features, which often differs from the mixed connective tissue type and which more closely resembles a sinonasal hemangiopericytoma-like tumor variant. Craniofacial PMT should be considered as a rare causative tumor in patients presenting with clinical and radiological features of oncogenic osteomalacia.